1. Field of the Invention
The present invention relates to a method and an apparatus for controlling the recirculation of exhaust gas for a Diesel engine, more particularly to a method of controlling the recirculation of the exhaust gas in an environment where the atmospheric pressure will change along with the change in the engine's geographical height from the sea, i.e. altitude and an apparatus for controlling the same.
2. Description of the Prior Art
The recirculation of the exhaust gas to the cylinders of the Diesel engine is such that part of the exhaust gas is taken out from the exhaust system and controlled for temperature, timing or flow rate for recirculation to the suction system, and it is therefore effective in the reduction of NOx. However, if the exhaust gas is recirculated in a low-pressure environment such as mountainous regions in the same manner as land at low elevation, white smoke is produced during the engine operation with a constant load, and in particular, during the idling of the engine.
Heretofore, to overcome this drawback, it has been proposed to use an atmospheric pressure sensor in which the output is changed depending upon the atmospheric pressure, thereby setting amount or rate of the exhaust gas recirculation at a reduced value when the Diesel engine is being operated at a high elevation.
The atmospheric pressure sensor according to the prior art was, however, disadvantageous in that it had a relatively large volume and accordingly a large space was required since the atmospheric pressure was measured by determining a mechanical displacement of a diaphragm or the the like used in the measuring unit, said mechanical displacement being due to a difference in the atmospheric pressure between the inside and the outside of the measuring unit. Furthermore, this measuring unit was not always accurate and the mechanically moving parts thereof were easily subject to malfunction. Accordingly, a simple method of measuring the atmospheric pressure with no mechanical movements is required. A further requirement is an atmospheric pressure measurement device which has an additional function, because the automobiles call for increasingly compact design and lower weight.